This patent specification relates to medical procedures such as ultrasound-assisted biopsies in which an invasive medical instrument such as a biopsy needle is guided by a medical imaging system such as an ultrasound system. More particularly, it relates to a low-cost apparatus for mounting the instrument to an imaging probe, controlling its position, monitoring its position, and/or predictively displaying its position on a user display of the medical imaging system.
Ultrasound imaging systems have become increasingly popular for use in medical applications because they are non-invasive, easy to use, capable of real-time operation, and do not subject patients to the dangers of electromagnetic radiation. Instead of electromagnetic radiation, an ultrasound imaging system transmits sound waves of very high frequency (e.g., 1 MHz to 15 MHz) into the patient and processes echoes from structures in the patient""s body to derive and display information relating to these structures. Although the preferred embodiments are described infra with respect to an ultrasound imaging environment, it is to be appreciated that they are also applicable in the context of other medical imaging environments including computerized tomography (CT), magnetic resonance imaging (MRI), and other environments.
Among other useful applications, ultrasound imaging systems are used in invasive surgical procedures such as biopsies. In such a use, the ultrasound imaging system is used to locate a region of interest in the patient, such as a tumor, and to assist the doctor or other medical professional (hereinafter xe2x80x9cuserxe2x80x9d) in guiding a biopsy needle to the tumor. As known in the art, ultrasound imaging systems generally only provide an image of a single plane within the patient as determined by the position and orientation of the ultrasound probe head. In particular, the imaged plane is usually a plane defined by the intersection of two lines, the first line being along a transducer array surface of the probe head, the second line being perpendicular to the first line along a center axis of the probe head. It is necessary to keep the biopsy needle positioned within the imaged plane in order for it to remain visible on the ultrasound monitor during the procedure.
Biopsy needle guides have been proposed for attaching biopsy needles to ultrasound probes and restricting movement of biopsy needles to the imaged plane. FIG. 1 illustrates a needle guide 100 proposed in U.S. Pat. No. 5,623,931, which is incorporated by reference herein, in which a probe clip 110 attaches to an ultrasound probe, and in which the biopsy needle is slidably guided by one of three grooves 111, thereby constraining its movement to within the imaged plane. FIG. 2 illustrates a needle guide 19 proposed in U.S. Pat. No. 4,899,756, which is incorporated by reference herein, in which the needle is rotatably affixed to a two-link structure that is, in turn, rotatably affixed to the ultrasound probe. The two-link structure comprises an xe2x80x9cascending linkxe2x80x9d 22 affixed to the ultrasound probe that is rotatable only in the imaged plane, and a xe2x80x9cdescending linkxe2x80x9d 23 that is slidably affixed to the ascending link and rotatable only in the imaged plane. The biopsy needle is thereby constrained to the imaged plane.
The medical realities of many biopsy procedures, including breast tumor biopsy procedures, render the needle guides of FIG. 1 and FIG. 2 insufficient for many practical situations. Many breast tumor biopsy procedures require a substantial number of different samples or insertions into the tumor, often at incrementally different positions and/or angles. It is often desirable to allow the user to maintain the probe head in a fixed position, thereby keeping the tumor position constant on the ultrasound output screen, while gently and incrementally adjusting the positioning and angle of the needle. As another example, because it is crucial not to puncture the chest wall and lung during the procedure, it is often desirable to insert the needle into the patient at an angle that is approximately parallel to the transducer surface, i.e. at an angle that is approximately 90 degrees from the probe axis. In this way, the ultrasound probe may be placed at a stable position perpendicular to the chest wall on top of the breast, while the needle is inserted at an angle parallel to the chest wall, thereby reducing the possibility of chest wall and lung puncture. Even further, it is desirable to have the ability to place the transducer surface on one side of the breast, while allowing the biopsy needle to be inserted on the other side of the breast, whereby the biopsy needle may enter the breast at an angle up to 180 degrees with respect to the probe axis. Still further, it is often desirable to insert the needle at a direct zero-degree angle with respect to the probe axis at a point directly adjacent to the transducer array.
While the needle guide of FIG. 2 allows more freedom of needle movement than the device of FIG. 1, it nevertheless presents substantial restrictions on needle movement and position within the imaged plane. For example, the two-link device is not readily amenable to allowing the zero-degree insertion (i.e., parallel to probe axis) of a biopsy needle at a point adjacent to the probe head, or of allowing a 180-degree insertion at a breast point opposite the probe head. It would be desirable to provide a biopsy needle guide that allows for substantially unfettered freedom of movement of a biopsy needle within the imaged plane of an ultrasound system, both in terms of needle angle and needle entry point.
Moreover, because a biopsy needle represents a thin, and often specular, target for the ultrasound system, it is often difficult for the ultrasound system to maintain a clear output image of the biopsy needle that is easily viewable. A clear image of the biopsy needle can be difficult to obtain even if its movement is restricted to the imaged plane. One method for dealing with this problem involves the performance of image recognition algorithms on the ultrasound image to identify and segment the biopsy needle, with the needle position and orientation then being highlighted on the display screen. The needle highlight usually comprises a bright-colored or otherwise noticeable line positioned at the computed needle position. Unfortunately, the image recognition algorithms often require extensive processing power, and output frame rates can suffer accordingly. Also, these image processing algorithms can at least partially fail if the needle wanders from the imaged plane. Finally, because of the appreciable amount of computation required, quick movements of the biopsy needle can cause jittery and/or delayed needle highlights.
Another method for dealing with needle visualization problems during ultrasound-assisted biopsy procedures is to mount three-dimensional position and orientation sensors, such as magnetic sensors, on the ultrasound transducer and the biopsy needle handle. The position and orientation sensors provide the position (x,y,z) and orientation (xcfx81,xcex8,xcfx86) of both the transducer and the needle handle to the ultrasound system. This allows for prompt computation of the position and orientation of the biopsy needle relative to the ultrasound image slice being displayed. The biopsy needle is manipulated xe2x80x9cfree-handxe2x80x9d and can depart from the imaged plane, with special designations on the highlighted display to indicate departure from the imaged plane. An example of one such system is the UltraGuide(copyright) 1000 available from UltraGuide, Inc. of Lakewood, Colo.; see also U.S. Pat. No. 6,216,029, which is incorporated by reference herein.
One or more practical disadvantages, however, are associated with systems based on three-dimensional position and orientation sensing. First, although they allow for xe2x80x9cfree-handxe2x80x9d operation of the biopsy needle, the three-dimensional sensing hardware is quite expensive, whether it be based on magnetic sensing systems, accelerometers, or gyro-based systems. Second, in several medical procedures including breast biopsies, it has been found that xe2x80x9cfree-handxe2x80x9d operation of the biopsy needle is often less desirable, with users preferring to be assisted by a mechanical needle support/constraint. Third, for many users the experience can be awkward and overly complicated, as they are required to simultaneously (i) manipulate the ultrasound transducer with one hand, (ii) manipulate the unsupported, unconstrained biopsy needle with the other hand, and (iii) observe and interpret needle highlights that are not always intuitive to understand. This is especially problematic because the unconstrained xe2x80x9cfree-handxe2x80x9d needle will often depart from the imaged plane, requiring the user to interpret special markings on the two-dimensional ultrasound display in trying to visualize the three-dimensional events. One attempt to remedy this problem is found in the UltraGuide(copyright) 1000 system, in which an animated three-dimensional perspective view of the needle and the imaged plane is placed beside the two-dimensional ultrasound slice. However, this requires the user to observe and interpret yet another computer output simultaneously with all of the other actions and observations then occurring. This can be an excessive requirement even for sophisticated users. Moreover, this also entails an additional layer of computational complexity for the ultrasound system. Fourth, because of the expensive nature of the three-dimensional sensing equipment involved, this equipment needs to be reused over many patients. This can increase the risk of contagious disease transmission unless careful sterilization and/or prophylactic measures are taken after each and every patient.
Accordingly, it would be desirable to provide a probe-mounted instrument guide for facilitating medical procedures in which an invasive medical instrument is guided by a medical imaging system, the probe-mounted instrument guide the allowing for substantially unfettered freedom of movement of the instrument within an imaged plane of a medical imaging system, both in terms of instrument angle and instrument entry point.
It would be further desirable to provide a probe-mounted instrument guide and position monitor for facilitating such medical procedures, the guiding and monitoring apparatus being easy and intuitive to use.
It would be even further desirable to provide such a guiding and monitoring apparatus that is low in cost to produce, such that it can be disposed of after a single use, thereby reducing risk of contagious disease transmission among successive patients.
According to a preferred embodiment, a probe-mounted instrument guide is provided comprising a plurality of rigid links or segments, including a first segment connected to the probe, a final segment connected to a handle of the instrument, and one or more intermediate segments coupled therebetween. The segments are hingeably coupled such that movement of the biopsy needle is restricted to the imaged plane. Preferably, there are at least three segments for allowing sufficient movement of the biopsy needle in the imaged plane, e.g., for allowing needle entry into the patient at a wide range of entry points and entry angles as required during many breast biopsies. The segments preferably comprise a low-cost but substantially rigid and easy-to-manipulate plastic material.
Advantageously, a needle-guiding apparatus in accordance with the preferred embodiments can be produced at very low cost, and therefore can be a disposable device. This is important in today""s clinical settings, in which medical imaging hardware can act as fomites for transmitting contagious diseases from patient to patient unless proper sterilization and/or prophylactic measures are taken. Here, the needle-guiding apparatus can simply be discarded along with the disposable needle and needle handle after the biopsy procedure.
According to another preferred embodiment, a low-cost apparatus is provided for also monitoring the position of a medical instrument while restricting its movement to the desired imaged plane. In another preferred embodiment, predictive monitoring of the position of the medical instrument is provided on a user display. According to a preferred embodiment, angle detectors are provided at each segment intersection. Information from the angle detectors is provided to the medical imaging system, which then readily calculates the position and orientation of the needle and superimposes a needle position indicator or highlighter on the user display.
Advantageously, in contrast to the sophisticated sensors required in three-dimensional free-space position detection systems, the angle detectors at the segment intersections can be procured at very low cost. Therefore, the needle guiding and position-detection apparatus can still be a disposable device. By way of example, the angle detectors may comprise low-cost position encoders such as optical position encoders or electrical potentiometers. Other angle detector types, such as those based upon angle-dependent inductive coupling or angle-dependent capacitive coupling, can be used. Optionally, for even further cost savings, the position encoders themselves can serve the mechanical coupling means between segments.
According to another preferred embodiment, the medical imaging system is configured to highlight the biopsy needle in a predictive manner, i.e., to display a projection of the needle based on its current position and orientation. Accordingly, even if the biopsy needle is outside the field of view of the imaged plane being displayed, its projection will appear on the display. This can be of great assistance in guiding the biopsy needle to the desired target location. If the biopsy needle is spring-loaded or is otherwise slidably coupled to its handle, an additional sensor on the needle handle provides the ultrasound system with this required data point.
The angle information corresponding to the respective link intersections may be transmitted to the medical imaging system in any of a variety of ways. In one preferred embodiment, which is likely to be the lowest-cost embodiment, electrical wires are connected to each angle encoder and run down the assembly to a common, standardized connector for connection to the medical imaging system. When there are several encoders, a common ribbon cable can be used to simplify the appearance and manipulation of the assembly. In other preferred embodiments, fiber optic cables can be used. In still other preferred embodiments, small RF transmitters, infrared transmitters, or optical transmitters may be used to communicate the angle information to the medical imaging system. A needle-guiding and position detecting apparatus in accordance with the preferred embodiments is readily applicable in ultrasound environments, computerized tomography (CT) environments, magnetic resonance imaging (MRI) environments, and other medical imaging environments.